Optical recording medium and process for producing the same, data recording method and data reproducing method for optical recording medium

Abstract

A supporting substrate 11 and a light-transmitting layer 12, and further between the light-transmitting layer and the supporting substrate 11 a dielectric layer 31, a noble metal oxide layer 23, a dielectric layer 32, a light absorption layer 22 and a dielectric layer 33 in this arranging order when viewed from the light-transmitting layer side are provided. The light absorption layer 22 contains as a main component a material that can be represented by (SbaTe1−a)1−bMAb (wherein MA is an element other than antimony (Sb) and tellurium (Te), 0<a<1 and 0≦b<1), and besides, that is different from an intermetallic compound represented by {(GeTe)c(Sb2Te3)1−c)}dMB1−d (wherein MB is an element other than antimony (Sb), tellurium (Te) and germanium (Ge), c is ⅓, ½ or ⅔, and 0<d≦1).

Description

TECHNICAL FIELD [0001] The present invention relates to an optical recording medium and a manufacturing method thereof, and more particularly, to an optical recording medium of the type which forms recording marks through the evolution of gas and a manufacturing method thereof. In addition, the invention is concerned with a method of recording data on an optical recording medium and a method of reproducing data recorded on an optical recording medium, and more particularly, with a method of recording data on an optical recording medium of the type which forms recording marks through the evolution of gas and a method of reproducing data recorded on such an optical recording medium. BACKGROUND ART [0002] In recent years, optical recording media, typified by CDs (Compact Discs) and DVDs (Digital Versatile Discs), have been widely used as recording media for recording high-volume digital data. [0003] With respect to the CDs, a compact disc of the type which can neither write data once m...

AI Technical Summary

Benefits of technology

[0022] In accordance with the invention, super-resolution recording and super-resolution reproduction can be performed at a λ / NA setting of 640 nm or below by use of a laser beam with a wavelength (λ) shorter than about 635 nm and an objective lens with a numerical aperture greater than about 0.6. Moreover, the main component in the light absorption layer is the foregoing material, so that the noble metal oxide layer has no inhibition in becoming locally deformed at the time of recording and it becomes possible to acquire excellent signal characteristics even when minute recording marks are formed.

[0023] In addition, it is preferable that platinum oxide (PtOx) is contained in the noble metal oxide layer. In this case, it is especially preferable that the noble metal oxide layer is constituted substantially of platinum oxide (PtOx), but there's nothing wrong with containing therein other components and inevitably mixed impurities. The use of platinum oxide (PtOx) as an component in the noble metal oxide layer makes it possible to obtain excellent signal characteristics and sufficient durability.

[0024] It is also preferable that the optical recording medium according to the invention further has a reflective layer provided between the supporting substrate and the third dielectric layer. By providing such a reflective layer, the level of reproduction signals is heightened and the reproduction stability is substantially enhanced as well. The term “reproduction stability” as used herein refers to the resistance to a deterioration phenomenon caused by reproduction, namely a phenomenon that the noble metal oxide layer changes its state by energy of a laser beam applied thereto at the time of reproduction and thereby a noise increase and a carrier decrease is caused to result in CNR reduction. The thickness of the reflective layer is preferably from 5 nm to 200 nm, far preferably from 10 nm to 100 nm, particularly preferably from 10 nm to 50 nm. By setting the reflective layer thickness at such a value, it becomes possible to achieve a sufficient reproduction stability enhancement effect without a big drop in productivity.

[0027] In accordance with the invention, it becomes possible to manufacture optical recording media which enable super-resolution recording and super-resolution reproduction to be performed at a λ / NA setting of 640 nm or below by use of a laser beam with a wavelength (λ) shorter than about 635 nm and an objective lens with a numerical aperture greater than about 0.6. Moreover, since the main component in the light absorption layer is the foregoing material, excellent signal characteristics can be obtained even when minute recording marks are formed. Moreover, since the main component in the light absorption layer is the foregoing material, excellent signal characteristics can be obtained even when minute recording marks are formed. It is preferable that the first process is carried out according to a vapor deposition method and the second process is carried out according to a spin coating method.

[0028] The data recording method according to the invention is a data recording method in which data is recorded by a laser beam being applied to the foregoing optical recording medium from the light absorption layer side, and is characterized in that, when the wavelength of the foregoing laser beam is represented as λ and the numerical aperture of the objective lens for focusing the laser beam is represented as NA, the λ / NA value is set at 640 nm or below and a recording mark train including recording marks λ / 4NA or below in length is recorded. On the other hand, the data reproducing method according to the invention is a data reproducing method in which data is reproduced by a laser beam being applied to the foregoing optical recording medium from the light-transmitting layer side, and is characterized in that, when the wavelength of the foregoing laser beam is represented as λ and the numerical aperture of the objective lens for focusing the laser beam is represented as NA, the λ / NA value is set at 640 nm or below and the data is reproduced from a train of recorded marks including the recorded marks λ / 4NA or below in length. In both cases, it is most favorable that the wavelength of the laser beam used is set at about 405 nm and the numerical aperture of the objective lens used is set at about 0.85. By doing so, the same recording-and-reproducing apparatus as used for next-generation optical recording media can be utilized, so the costs for development and production of recording-and-reproducing apparatus can be reduced.

[0029] In accordance with the invention, super-resolution recording and super-resolution reproduction can be performed at a λ / NA setting of 640 nm or below by use of a laser beam with a wavelength shorter than about 635 nm and an objective lens with a numerical aperture greater than about 0.6, and it becomes possible to obtain excellent characteristics in super-resolution recording and super-resolution reproduction, notably those using a laser beam with a wavelength shorter than about 405 nm and an objective lens with a numerical aperture greater than about 0.85 which are those used for next-generation optical recording media. Accordingly, the same recording-and-reproducing apparatus as used for next-generation optical recording media can be utilized, so the costs for development and production of recording-and-reproducing apparatus can be reduced.

Problems solved by technology

In the case of next-generation optical recording media, therefore, it is difficult to form various functional layers including a recording layer on a light-transmitting substrate as in the case of current optical recording media, such as CDs and DVDs.

However, the use of a laser beam of any shorter wavelength causes a sharp increase in absorption of the laser beam by a light-transmitting layer and intensifies deterioration of the light-transmitting layer with time, so it is difficult to use a laser beam with any shorter wavelength.

And it is also difficult to increase any further the numerical aperture of an objective lens in consideration of difficulty in lens design, provision for a tilt margin and so on.

In other words, it can be said that any further reduction in the beam spot diameter of a laser beam is extremely difficult.

However, as mentioned above, the mechanism for reproducing possibilities of data from marks of recording finer than resolution limit on super-resolution optical recording media is unknown, so that there is some question as to whether super-resolution reproduction is feasible or not in the case of using a laser beam with a wavelength shorter than 635 nm and an objective lens with a numerical aperture greater than 0.6 as well.

Since it in particular turned out that the phase-changing material layer hitherto regarded as “recording layer” didn't function actually as recording layer, there is a lot of uncertainty about what contributions the phase-changing material layer has to the formation of recording marks, what changes are caused in signal characteristics by materials used, and so on.

Images